Question about frostings

Halloween is right around the corner and I’m itching to make outrageous cupcakes! The cake part shouldn’t be an issue, but the frosting is.

Have you ever made a corn-free frosting? Which means powdered sugar is out of question. I’ve tried making my own with a coffee grinder, and it just didn’t get the texture I wanted. It was still grainy. No corn also means no marshmallow creme such as Fluff.